1. Field of the Invention
A system for reducing the electrical losses of an electro-hydraulic actuator used for aircraft control purposes.
2. Description of the Prior Art
The present Electro Hydraulic Actuator (EHA) for controlling aircraft components such as control surfaces comprises a Hydraulic Surface Actuator, powered by a DC Servo-motor driving a multi-piston constant displacement Bi-directional Hydraulic Pump and contains an electrical Actuator Feedback Sensor installed on the Actuator Piston Rod. The actuator servo input is an Electrical Command Signal coming from a computer that processes signals from cockpit controllers and control switches, from internal sensors in the airframe, from aerodynamic sensors and, in some cases, from external signals. This command signal is summed in a Summing Amplifier with the Actuator Output Position Voltage as detected by an Actuator Feedback Sensor. The difference between the input and the output voltage, the Error Signal is applied to the DC Servo-motor to drive the pump in a direction to hydraulically force the Actuator Piston Rod to reduce that error. Under no-load conditions, the actuator is driven to that position where the voltage from the Actuator Feedback Sensor equals the input voltage. When an airload is applied to the actuator, the actuator displaces the small amount needed to create an Error Signal voltage on the output of the Summing Amplifier equal to that voltage required to produce the motor winding current and the associated motor torque necessary to balance the applied load. When maximum actuator load is applied, this Error Signal voltage, as measured at the motor, equals the line voltage, and the motor current required to balance that load is line voltage divided by the DC resistance of the motor windings (stalled rotor current). The input power required to produce and maintain stall hinge-moment equals stall hinge-moment times maximum no-load surface rate (ft-lbs./sec.). This EHA design results in extremely high current draw and power losses at high hinge moments, particularly stall, resulting in high heat losses.